The invention relates to a rotary pump, to a hydrodynamic mixer with a rotary pump of this kind and also to the use of the rotary pump for the processing of suspensions.
In many industrial processes, for example in the manufacture of semi-conductors and chips, it is necessary to mix suspensions in a controlled manner and to dispense them via nozzles or similar apparatus. Chemical-mechanical polishing processes (CMP, chemical-mechanical planarization), such as are used in the semi-conductor industry, are named as an important example. In processes such as these a suspension, usually termed a slurry, made of typically very fine solid material particles and a liquid is applied to a rotating wafer and serves there for the polishing or lapping of the very fine semi-conductor structure. Another example is the application of photo-resist onto the wafer, or the roughening of the surfaces of computer hard drives, in order to prevent an adhesion of the print heads/read heads by means of adhesive forces, in other words, by means of Van der Waals forces.
A dispensing apparatus which is in principle suitable for this and is known from the prior art is illustrated in FIG. 1. In order to differentiate the prior art from the embodiments of the present invention, those features which relate to features of apparatus from the prior art are provided with single or double prime symbols in the drawings, whereas the features of embodiments in accordance with the invention are not provided as such.
The known dispensing apparatus 1′ of FIG. 1 includes a storage container 2′, which is filled with the fluid, e.g. slurry. The storage container 2′ has an outlet 4′ to which a pressure line 5′ is attached, which extends via recirculation pump R′ to an inlet 6′ at the storage container 2′. A plurality of extraction points 7′ are provided in the pressure line 5′ downstream of the recirculation pump R′, which lead to nozzles or other apparatus—usually designated as a tool—with which the fluid is applied, for example onto the wafers. Each extraction point 7′ is provided with a valve 8′, in order to open or to close the flow connection to the respective apparatus. If all extraction points 7′ are closed, the recirculation pump R′ merely effects a circulation of the fluid and thus a slight locally limited stirring of the fluid in the storage container 2′.
The desired pressure, with which the fluid is conveyed through the pressure line 5′ and the open extraction points and made available there, can be generated or influenced by pressure discharge of the fluid in the storage container 2′. In addition, an inlet 10′ is provided at the storage container 2′, through which a pressure medium can be brought into the storage container via a pressure control valve 11′, as illustrated symbolically by the arrow G. A gas, for example nitrogen, is usually used as a pressure medium, with which an overpressure of 0.5 bar, for example, is maintained in the storage container 2′.
An apparatus of this kind does have disadvantages however. In order to generate the overpressure in the storage container 2′, this has to be designed to be gas-tight, which is quite complicated apparatus-wise. Moreover, it is not straightforwardly possible, to fill new fluid into the storage container 2′, if the filling level becomes too low. A change of the pressure in the storage container 2′ and thus a change of the pumping pressure is also complicated and time-consuming. Furthermore, it is possible that the pressure medium (gas) enters the fluid or dissolves in the fluid, which can lead to undesired changes in the composition of the fluid.
However, a far greater problem, particularly in suspensions such as a slurry, for example, or in fluids which tend to separate or agglomerate, is to be seen in the fact that the circulation caused by the recirculation pump R′ is as a rule far too weak and irregular to guarantee a movement of the fluid everywhere in the storage container 2′ which is adequate for a constant mixing. For this reason, additional measures are often necessary in order to ensure an adequate movement or mixing of the fluid in the storage container 2′ in the long term.
In contrast to this the apparatus for the mixing and dispensing of a fluid proposed in EP 1 318 306 B1 and illustrated in FIG. 2 already represents a significant advance.
The dispensing apparatus 1″ of FIG. 2 proposed in EP 1 318 306 B1 can be used in a CMP process in the semi-conductor industry for example. In these processes, a suspension of fine solid material particles termed a slurry is applied on a rotating wafer in a liquid and serves there for the lapping or polishing of the very fine semi-conductor structures. The apparatus or tools not illustrated in FIG. 2 each include, for example, a nozzle or a different means by the use of which the fluid “F” can be applied to the wafer.
Within the context of this application the term “rotary pumps”, which are also called centrifugal pumps, covers all those pumps which have a rotor or a vane, through the rotation of which an impulse is transmitted to the fluid to be pumped. The term “rotary pump” includes in particular centrifugal pumps, axial pumps and side channel pumps. In a rotary pump, the inlet and the outlet are typically in constant flow connection. There are therefore no valves provided between the pump inlet and the pump outlet for example.
In the example of FIG. 2 known from the prior art, the rotor 31″ is arranged directly in the outlet of the storage container 2″ for the mixing of the fluid F″. The rotor 31″ projects at least partly into the storage container 2″ to mix the fluid F″.
That is to say, this is a rotary pump with an open pump housing and not a rotary pump with a closed pump housing.
Thus the rotary pump 3″ not only serves for the pumping of the fluid F″, but above all as a stirrer, which mixes the fluid F″ in the storage container. To this end the rotor 31″ has a plurality of vanes 311″ which are designed to be considerably larger than in known rotary pumps of comparable dimensions. The vanes 311″ reach into the storage container 2″ and ensure here (on rotation of the rotor 31″) a certain circulation of the fluid F″, as is suggested by the arrow Z″.
The rotor 31″ is arranged in a rotor housing 312″, which forms a part of the wall of the storage container 2″. The open, not closed, rotor housing 312″ is an integral part of the storage container 2″ here. It can also be secured to this as a separate part.
The rotary pump 3″ further includes a stator 32″ with a stator coil 322″ to electrically drive the rotor 31″. The stator 32″ surrounds the rotor housing 312″ and the stator 32″ is designed as a stator of a so-called temple motor. This means that the stator 32″ has a plurality of stator teeth connected by means of a flux return member, with each stator tooth being formed in an L-shape with one short limb and one long limb. The longer limb extends in each case parallel to the axis of rotation of the rotor and the shorter limb extends radially inwardly in the direction towards the rotary axis. The longer limbs carry the stator winding 322″.
The apparatus of FIG. 2 further has a pressure line 41″, through which the fluid F″ can be pumped to the apparatus and tools already mentioned above and not illustrated in FIG. 2, by which the fluid F″ can be brought onto a wafer, for example.
In order to achieve a notable through mixing of the fluid 2 with the apparatus of FIG. 2, it is essential that additional fixed vanes 21″ are provided in the storage container, which first make a through mixing of the fluid F″ in the operating state possible at all.
The reason for this becomes easily recognizable if one looks at an apparatus in accordance with FIG. 2a, which does not have any vanes 21″ in the storage container. An apparatus of this kind is illustrated in FIG. 2a in a simplified manner.
The apparatus of FIG. 2a likewise includes a storage container 2″ for a fluid F″. A rotary pump 3″ with a rotor 31″ is provided at the base of the storage container 2″. The rotor 311″ rotates in the direction of the arrow 3000″ in the tank 2″. The pressure line 41″ is not illustrated for reasons of clarity.
The only fundamental difference between the apparatus of FIG. 2a and the one illustrated in FIG. 2 is thus that the vanes 21″ are absent.
The absence of the vanes 21″ has massive consequences in the apparatus of FIG. 2a, as regards the ability to thoroughly mix the fluid F″ in the container 2″ of FIG. 2a. A through mixing of the fluid in the storage container 2″ of FIG. 2a does not take place at all in practice.
This is because of the fact that the fluid F″ in the storage container is coupled to the rotation of the rotor 31″ and the fluid F″ in accordance with the arrow P″ is set into rotation in the same direction as the direction of rotation 3000″ of the rotor 31″, so that an eddy V″, with a funnel-shaped liquid surface, also called a vortex V″, forms in the container. Since at least near the rotor 31″, or in the vicinity of the center of the storage container 2″, the rotating vortex V″ adopts approximately the rotational speed of the rotor 31″, practically no more eddying takes place in the fluid F″ and thus essentially no through mixing of the fluid F″.
If, then, a good through mixing of the fluid F″, which is preferably a suspension F″, such as for example a slurry F″, is to be guaranteed, vanes 21″ as shown in FIG. 2 have to be provided, which prevent the formation of a stable vortex V″, i.e. break up the rotating flow of fluid.
The disadvantages of the solution known from the prior art for a mixer in accordance with FIG. 2 are many. The construction is complicated, expensive and inflexible because the vanes 21″ are essential in the storage container 2″. That does not just mean a more complicated construction but also more complicated servicing because, for example, during work on the motor, the vanes have to be removed and inserted again in a complicated manner. The cleaning of the plant is made correspondingly difficult and the construction is ultimately expensive, not only as regards the acquisition, but also as regards repairs and servicing.
A far more serious disadvantage, however, is the inflexibility, conditioned by its construction, of the apparatus, known from the prior art. The important parameters, which determine the mixing process and, if a pressure line 41″ is present, the pumping process, are substantially determined by the geometry of the apparatus or by the parts from which it is assembled. Thus, for example, the intensity or the quality of the through mixing of the fluid F″ and 7, or the pumping power of the rotor 31″, can only be influenced by the speed of revolution of the rotor 31″ within certain limits, if at all. The hydrodynamics of the through mixing can hardly be adapted; that is to say, the distribution, size and geometry of the eddy in the storage container 2″ are substantially determined by the geometry of the vanes 21″, their size and arrangement in the storage container 2″ and also the further components and parts of the storage container.
An adaptation of the apparatus in accordance with FIG. 2 to the mixing process, to the requirements, to the different fluids F″ or to different mixing conditions, such as for example temperature, viscosity of the fluid F″ etc., is not possible without considerable structural change.
Moreover, the pumping process and the mixing process are strictly coupled to one another and cannot be adapted without constructional changes.